Hydrogen gas, in particular, is used in vast quantities for numerous industrial applications. The demand for hydrogen is increasing, particularly as hydrogen is increasingly being pursued as an ideal fuel source.
By far, the most common processes for producing hydrogen gas involve the reaction and breakdown of fossil fuels. Some examples of these types of processes include steam reforming of natural gas and coal gasification. However, these processes have the significant disadvantages of relying on a non-renewable and polluting resource. In particular, large quantities of carbon monoxide and carbon dioxide are generally produced in fossil fuel-based methods for hydrogen production. Accordingly, there is considerable interest in finding cleaner methods for the large-scale production of hydrogen.
One possible alternative method is the electrolysis of water. The electrolysis of water produces hydrogen and oxygen gas without the production of toxic and environmentally unfriendly byproducts. Moreover, since the electrolytic method uses electricity as the power source, another advantage of the electrolytic process over hydrocarbon processes is its amenability in receiving electrical power from a renewable source, such as solar, wind, or hydroelectric power. Some patent references directed to electrolysis technology include, for example, U.S. Pat. Nos. 7,601,308, 7,550,068, 7,510,633, 7,459,065, 7,452,449, 7,270,908, 7,241,950, 6,855,450, 6,613,215, 5,968,325, 5,667,647, 5,665,211, 5,534,120, 5,268,081, 5,089,107, 5,037,518, and 4,737,249, and U.S. Application Publication Nos. 2010/0206722, 2010/0101941, 2009/0325014, and 2008/0264780.
The electrolysis of water involves the decomposition (i.e., “splitting”) of water into oxygen and hydrogen gas by the action of an electric voltage (i.e., current) being applied to the water across electrodes of opposite polarity. Hydrogen is produced at the negative electrode (cathode) and oxygen is produced at the positive electrode (anode), as shown by the following well-known chemical equations:Cathode (reduction): 2H+(aq)+2e−→H2(g)Anode (oxidation): 2H2O(l)→O2(g)+4H+(aq)+4e−
Although the electrolytic process has the advantage of more cleanly producing hydrogen and is amenable to being powered by renewable sources, the electrolytic process remains non-competitive with conventional hydrocarbon processes because of the labor-intensive and materials cost of conventional electrolyzers as well as the prohibitive cost of current precious metal electrodes (e.g., complex platinum plates or honeycombs) used in electrolyzers of the art. Therefore, since hydrogen can be produced more affordably from fossil fuels, electrolytic processes for producing hydrogen have generally been limited to small-scale operations.
Yet, it has been estimated that in a future hydrogen economy, electrolyzers 10 to 100 times the size of today's largest units would be needed (Ivy, J., “Summary of Electrolytic Hydrogen Production”, National Renewable Energy Laboratory, NREL/MP-560-36734). Moreover, such large-scale electrolyzers would be greatly beneficial at the present time to take the place of existing hydrogen production technologies. Clearly, state-of-the-art electrolysis technology is significantly deficient in producing such large-scale amounts of hydrogen and oxygen in a clean and cost-effective manner.